WASHINGTON (REUTERS) - The US Embassy in Kyiv urged American citizens in Ukraine to consider departing now, saying that the security situation in the country was "unpredictable due to the increased threat of Russian military action."

The security situation in Ukraine "can deteriorate with little notice", the embassy said on its website on Wednesday (Jan 26).

In Washington, Secretary of State Antony Blinken said the US Embassy in Kyiv would remain open but added that Americans in the former Soviet country should "strongly consider leaving."

Earlier this week, the United States urged its citizens not to travel to Ukraine.

The US delivered written replies on Wednesday to sweeping Russian security demands, a key step in a fragile diplomatic process as Russia staged new military drills on land and sea near Ukraine.

US President Joe Biden said on Tuesday that personal sanctions on Russian President Vladimir Putin, though a rare step, could be considered as part of a drive by Washington and its allies to convince Moscow that any new aggression against Ukraine would have swift and massive costs.

Russia warned on Wednesday that imposing sanctions on Putin personally would not hurt him but would be "politically destructive."

Russia has gathered tens of thousands of troops near its border with Ukraine but has denied that it plans to invade.

The US has spent weeks trying to build agreement with European partners on a strong sanctions package if Russia attacks.